One of the most common electric scooter parts that need to be replaced, the CDI module is as essential to the scooter’s ignition system as the spark plug. Considered the brainchild of the brilliant Nikola Tesla, Capacitor Discharge Ignition (CDI) is the standard system used in most gasoline powered scooters today, as well as many motorcycles, marine outboards, and other small engines. A complete CDI module is made up of a transformer, the charging circuit, the rectifier, a capacitor, and the trip circuit.
How the CDI module works
The transformer first raises the voltage from 400 to 600 volts. Moving along the charging circuit, the electric current charges the capacitor, and the rectifier prevents the capacitor from discharging before the on point. Upon receiving the drive signal, the drive circuit stops charging and allows the capacitor to discharge in the low inductance ignition coil. This increases the discharge of the original 400-600 volt capacitor up to 40 kV in the secondary winding, bypassing the spark plug gap and igniting the gas / air mixture in the cylinder. Then the charging circuit is reconnected and resumes charging the capacitor again.
AC or DC?
Most of today’s scooters use an alternating current (AC) system; However, the popular scooter brand KYMCO uses direct current (DC). As a result, electric scooter parts for KYMCO machines, including the CDI module, can sometimes be difficult to find.
Machine size
It is always best to match the engine size to the CDI specification. A CDI module made for a 50cc engine. could They run on a 100cc, 125cc, or 150cc engine, and some are designed to run on a variety of engine sizes. Others, however, will only work for a particular engine displacement. Always check the specs to make sure you get the correct scooter ignition parts.
2 and 4 stroke scooter ignition
2-stroke and 4-stroke engines are completely different and as a result the ignition timing of their engines is also totally different. You cannot use a CDI made for a 2-stroke engine on a 4-stroke scooter. In contrast, you cannot use the CDI of a 4-stroke scooter on a 2-stroke scooter.
Connectors
In many current CDIs, the connectors are an integral part of the unit’s housing, forming a plug that fits directly into the scooter’s wiring harness. In other models, the connectors can be located on cables, allowing some room for maneuver in the exact place where the module is mounted. The skilled mechanic can shorten or lengthen these cables as needed. The most common CDI connector style uses two plugs side by side; a 4-pin plug and a 2-pin plug. These connectors can be square, rectangular or simple.
Note: Photo illustrations of many CDI connectors can be viewed on the website listed at the end of this article.
Unrestricted or restricted?
An unrestricted (or racing) CDI provides current no matter how high the engine RPM is. As the CDI controls the spark plug, the spark plug will continue to fire at high RPM. For reasons that should be obvious, these CDI units are made for racing use and are not very suitable for regular road use. However, a restricted CDI module will stop firing once the preset engine RPM is reached. Without current reaching the spark plug, the engine RPM drops below the preset limit and only then will the CDI resume supplying current to the spark plug.
When replacing a CDI module, or any other scooter ignition or electric scooter parts, it is always a good idea to consult your owner’s manual. If the manual is lost or missing, many manufacturers and brands have downloadable manuals available on their websites.
